Stainless Anchor Chain

[colemj]

Originally Posted by Mark Johnson

This 1/4" G-4 galvanized chain has a 2,600# SWL, according to ACCO! (Breaking strengths are irrelevant). NO SS chain, of similar size and weight to mine, even comes CLOSE to this WL. If it did, I would've used it!

Mark

You need to define the terms of comparison. ACCO sets their safe working loads on their G4 chain as 1/3 of the certified breaking load. All other companies set it at 1/4 of the certified breaking load.

You cannot measure a SWL, only a breaking load. You can only calculate a SWL from the BL. SWL are only relevant when the calculation parameter used is stated. BL become VERY relevant as you approach a high load on your gear.

So the only measurement that actually matters is the certified test load causing the chain to break. In other words, the breaking strength. SWL is calculated off of this using either a 1/3 margin (ACCO) or a 1/4 margin (everyone else).

The most common SS grade used in anchor rode is Grade 50, which is stronger than Grade 40. By definition, G5 SS is certainly stronger than G4 galv.

The common Grade L SS would need to be compared to G3 galv, not G4, and it shouldn't be used in anchor rode anyway unless you are absolutely positive its composition, provenance and manufacturing quality is suitable.

The confusion is due to a lot of different SS chains out there that show up in a simple google search for SS chain. These chains are inappropriate for anchoring.

The weight of G5 per unit is the same as that for G4, if not a tiny bit less.

So let's do a true comparison of 5/16" G4 galv with G5 SS (info from Maggi chain):
SS: BL 11,000lbs, SWL 2,750lbs, Weight: 3lbs/meter
Galv: BL 8,900lbs, SWL 2,225lbs, Weight 3lbs/meter

I don't think anyone really makes a G5 SS anchor chain in 1/4". Most start at either 5/16" or 3/8". So you probably don't even have a SS option that I would trust.

BTW, I am not being argumentative here. But SS is perfectly acceptable as anchor chain as long as one gets an appropriate product. This is no different for galvanized chain with the exception that appropriate galvanized anchor chain is readily available and well understood by the community.

You wouldn't just go to your local hardware store and pull a bunch of Chinese proof coil galvanized out of the bin for use as anchor chain, the same way you wouldn't do so for SS.

Mark

[GordMay]

Originally Posted by colemj

... The confusion is due to a lot of different SS chains out there that show up in a simple google search for SS chain. These chains are inappropriate for anchoring...

... SS is perfectly acceptable as anchor chain as long as one gets an appropriate product. This is no different for galvanized chain with the exception that appropriate galvanized anchor chain is readily available and well understood by the community.

Indeed.

[Bash]

Originally Posted by colemj

You made a mistake on the galv. BBB, it is 1900lb SWL. The spec listings on WM's website are very confusing and run together.

Thanks for pointing out my mistake.

[Mark Johnson]

Colemj.. Mark, (nice name)

As I said before, in ALL marine gear, breaking strength is TOTALLY irrelevant! It tends to only confuse the issue, and is used mostly as marketing hype. It sounds like you might have fallen for it? Each manufacturer determines what the safe working load is, based on the material used, the method of production, its abrasion resistance, its projected working environment, moving parts, projected lifespan, danger to human life if it fails, etc etc.

It is not just a matter of company "X" defines it at a certain % of BL, and company "Y" would define the EXACT same product at a different % of the same original BL. There are other considerations at play...
With different chain products, within the same company, they will often come up with a different % of their breaking loads, depending on ALL of the above criteria.

Acco might use 1/3 of BL, where as another company might use 1/4 of BL, because ACCO considers their manufacturing technique superior, and decades of testing have made their engineers as well as legal team, comfortable with this safety factor. Another chain company, with the exact same original BL chain product, might use 1/4 of BL, because it is not as reliable a material or process, OR with a shorter track record, IN THIS PARTICULAR APPLICATION, this is what their legal team is willing to assure it's customers of. None of these numbers are etched in stone! It is all just their best projections. In our modern world, ripe with legal paranoia, they are ALL trying to "be very conservative", without loosing sales from too weak a product SWL, by comparison. They are in other words, trying to get the proper SWL "just right". This SWL is, therefore, all that we have to go on, and all that really matters.

The safe WORKING load is the maximum that You should ever expose the chain to long term! It only complicates and confuses the issue to say: "But, with NO shock load OR wear, no UV or salt exposure, and as tested in a lab, THIS one had a higher BREAKING load" than that one.

Sometimes one chain might have a higher BL than another's BL, but actually be the weaker chain, (in the projected real world application). It depends on ALL of the above criteria...

I have several friends with bare aluminum boats, (one a brilliant German engineer). Just like we did, they built their boats, and they all have SS chains. This is where I saw their advantages first hand. I really like the stuff, and clearly said so in my first post on this thread. It is particularly useful where you can go up a size if necessary, to match the SWL to what the boat requires, minimizing extra weight doesn't matter, and galvanic compatibility does matter.

My years of research about this was for OUR boat and situation... I have learned however, that the stronger alloys of SS are frequently the least corrosive resistant. This is why when one goes up in quality from 304 SS standing rigging to 316SS, they need to consider going up a size. There needs to be both strength AND longevity, through years of continuously sitting on the bottom.

In my size chain, (1/4" G-4) with a custom 3/8" oversized end link, I have an ACCO certified SAFE WORKING LOAD of 2,600 pounds. This is day in day out, continuous loads, in real life cruising conditions...

G-4 is not even the strongest HT chain! It is just what is most easily available, of the "stronger" chains, and has a track record, (in this application), involving tens of thousands of customers. If you go with a chain stronger than G-4, that has more strength than all available shackles, you gain nothing!

Perhaps I have been wrong in my research? Please help... I would like to look up this: "custom made 1/4" SS chain with a single 3/8" oversized end link. It would be made of a very non corrosive alloy of SS, it would also match my current G-4 gypsy, and have a decades old certified SWL of > 2,600 pounds, yet weigh the same or < my G-4 chain, AND be backed by a history of successful use by tens of thousands of customers in this ocean anchoring application".

I have searched for years, and never found it.

Some things are different for different sizes of chain. For example... Crosby makes a galvanized 3/8" HT shackle, which will connect up to ACCO galvanized 5/16' G-4 / HT chain. They are strength compatible.

In my size chain however, (1/4" HT), Crosby does not make a strength compatible 5/16" HT shackle that is as strong as the chain. This is why I paid to have an oversized link made into the end of my 1/4" chain. Now, my entire system is strength compatible.

If yours anchoring system is as well, you are ahead of the game. GREAT! I actually would seriously consider SS chain, for all of the advantages that I mentioned. So, if you would send me a link on how to replace my galvanized at the same or less weight, and same or more SWL, I'd appreciate it. Honestly, however, I don't think it exists...

Thanks much, Mark

[Hud3]

Interesting article here, Connectors, where they tested various anchor chain and connector combinations. Their conclusion...

• Galvanised carbon steel chain was stronger than the stainless steel chain tested.
• The stainless steel fracture suggested it to be less ductile than the carbon steel and therefore more prone to fracture on impact.
• C-links for joining lengths of chain were less than half as strong as the chain.
• Five of the connectors tested had strength equivalent to the chain. Four of these were the clamped type in which the connecting screw was not load-bearing. These were all made in stainless steel. The fifth was a fixed type made in carbon steel.
• Galvanised steel shackles that are specified for lifting and hoisting duties had the highest strength but their results were variable.
• Stainless steel shackles were consistently stronger than equivalent galvanised steel ones.

It's curious to me that the galvanized chain was stronger than s/s, but the reverse was true for shackles.

[Mark Johnson]

Interesting Hud,

To connect up our one oversized 3/8" chain link to the anchor, I didn't like the size and "clunkeyness" of an ACCO HT swivel with Crosby HT shackle. They were strength compatable, but didn't appeal. So, I got a fancy SS "ball and socket" connector @ > $200! (ouch!) Luckily it was NOT one of the re-called brands...

Other than promoting rust where tha galvanized meets the SS, It has held up perfectly... M

[GordMay]

Definitions from the NACM Welded Steel Chain Specifications:

“3.1 Working Load Limit (WLL)
The "Working Load Limit" (rated capacity) is the maximum load that shall be applied in direct tension to an undamaged straight length of chain.

Gord's note: A number of factors, including exposure to salt water, can reduce the listed WLL

3.2 Proof Test
The "Proof Test" (manufacturing test force) is a term designating the minimum tensile force which has been applied to a chain under a constantly increasing force in direct tension during the manufacturing
process. These loads are manufacturing integrity tests and shall not be used as criteria for service ordesign purposes.

3.3 Minimum Breaking Force
The "Minimum Breaking Force" is the minimum force at which the chain during manufacture has been found by testing to break when a constantly increasing force is applied in direct tension. Breaking force values are not guarantees that all chain segments will endure these loads (see Section 5.2). This test is a manufacturer's attribute acceptance test and shall not be used as a criterion for service or design purposes ..."

Here ➥ http://www.nacm.info/Downloads/NACM%20_Welded_Specs.pdf

To which Peerless-ACCO adds:

"... The Working Load Limits and the associated safety factor of each Peerless product may be affected by wear, misuse, overloading, corrosion, deformation, intentional alteration and other use conditions. Regular inspection must be conducted to determine whether use can be continued at the assigned Working Load Limit, a reduced Working Load Limit or whether the product must be withdrawn from service. The terms “Working Load Limit”, “Proof Test” and “Minimum Breaking Force” contain no implication of what load the chain will withstand if the chain is used in such conditions of abuse and misuse. Peerless Industrial Group accepts no liability for any such abuse or misuse.

The Working Load Limit of a sling or assembly must not exceed the lowest Working Load Limit of the components in the sling or assembly. Use only Peerless Industrial Group approved parts as replacements when servicing or repairing original Peerless Industrial Group slings or assemblies ..."

Here ➥ Cautions & Warnings, Safety Guidelines, Temperature & Chain, Table of Wear

Working load limit (WLL), safe working load (SWL) and minimum and maximum rated loads explained
➥ http://www.irata.org/uploads/healthandsafety/WLLSWL.pdf

[colemj]

Hi Mark,

Two things for clarity: I don't have SS anchor chain - it is way too expensive for me - and I mentioned in another post that good SS chain doesn't appear to be available in 1/4" short link, so you won't have any option there and can stop searching for it. If you chose to move up in size, you will have good options in SS.

I'm sorry, but I have to disagree and think you have things backwards. When looking at a catalog, BL's are the only (mostly) real numbers. They are an indication of the grade of chain you are buying. The SWL should be a number corresponding to an actual test, but it is often not.

Proof loads are just that - tested to not break at that load. ACCO pulls a bit of marketing by proofing at 1/3 of BL and calling it HT which, in their parlance, means "High Test".

HT in everyone else's world means "High Tensile" and is a description of the physical grade of chain - usually starting at Grade 70.

The SWL ratio chosen has nothing to do with a company's confidence in their product, the length of time it has been a product line, or its reliability. 1/4 BL is solely a standard in use for a very long time. ACCO decided for marketing reasons to pull their proof tests a bit further to 1/3 BL, call it a SWL, label it "HT" and carve out a niche.

Look around at all other chain manufacturer's around the world - NONE of them use 1/3 BL. ACCO stands alone on this piece of marketing. There is nothing wrong with what ACCO is doing, unless it leads someone to make a decision based on the SWL instead of the grade of chain, the quality of the manufacturing and the intended use.

And trust me, there are better quality chains out there than ACCO.

So your reasoning for the differences in SWL among manufacturers sounds good, but just isn't correct. The chain world IS standardized, but ACCO just takes a few acceptable liberties with terms of the standardization.

Regardless of what it is called in marketing, all chain resolves into standardized grades, which are a function of their metallurgy and are indicative of their strengths.

So G4 may be proof tested by ACCO to a different ratio of breaking strength than other manufacturers, but if you look at the tested breaking strengths of all chains in a given grade, you will find them to be pretty close to equal.

That is why ACCO's breaking strength is the same as Maggi's.

The only way one can have any type of true confidence in a chain is if they have seen the actual proof certificate for the individual batch of chain from which they are purchasing their lot. Any general number in a catalog is just that - a general number.

If you did not see this certificate, your confidence in your chain is misplaced and you are relying solely on the reputation of the company (which is how most of us buy most things, if you think about it).

So, going back to the debate on SS vs galv regarding strength. G5 SS is stronger than G4 galv. This is a matter of metallurgy. You can easily find poor and good manufacturing examples of both.

If you are still concerned about the SWL number, simply have the company proof test it to 1/3 BL like ACCO. All reputable manufacturers will do that.

I am surprised about your friends with aluminum boats. SS and aluminum are further apart galvanically and I would expect the zinc on galv chain to protect the aluminum more than SS.

There use to be a chain guru posting here by the name of GMac. He is very involved in the chain industry and a perusal of some of his past posts would be enlightening.

If you want to hear of some ACCO G4 chain woes, I have a tale to tell, along with 19 other people I met in ONE ANCHORAGE this year with the same tale. SWL is meaningless if your chain is flaking sheet rust and splitting open after 6 months... (the resolution of which involved my long and detailed education in the art, science and witchcraft of chain manufacturing, grading and marketing - I'm not making this stuff up, I have been immersed in it for months).

Mark

[ShipShape]

Originally Posted by At sea

Re para 2, wouldn't the oxygen in the water replace the 'oxide skin' on stainless chain as soon as it is scratched, rather than create a galvanic cell? I always thought that a benefit of stainless fittings was that a scratch or gouge didn't start any degradation...

True - if the oxide skin is damaged the chromium in the SS reacts with oxygen in the air or water "healing" the damage by reforming the chromium oxide skin. This skin is very tough, and to quote from Everett Collier's "Boatowner's Guide to Corrosion," "...not even seawater is aggressive enough to cause the protective passive film that forms on [austenitic stainless] steels to break down. The trouble comes when the film is scratched or otherwise damaged, or when there is insufficient oxygen present at the surface for the film to form."

Areas beneath organic growth and buried in the mud will be oxygen starved and unable to reform the oxide skin. Type 316 is about twice as resistant to pitting and crevice corrosion as 304, and under "good" conditions it is possible to use 304 in water with up to 1000 ppm chloride concentrations, which is about the max chloride concentration you will see in a freshwater river. Seawater has a chloride concentration of about 19,000 ppm. When you scratch the oxide skin in seawater, an aggressive galvanic cell gets going, actually driven by oxygen (according to Nigel Warren) and there is no stopping it. The voltage difference between the passive oxide skin and the active pit can be as much as 0.5 volt.

This is why you do not see stainless hardware such as thruhulls used near or below the waterline, and what is used underwater, such as propeller shafts and rudder stock, needs cathodic protection.

Another quote from Everett Collier, "Type 316 ...in many instances has been used successfully immersed in seawater. However, ... the seawater must be clean, unpolluted, free of mud and silt, continuously moving with a velocity of not less than 3 ft./sec. over the entire surface of the fitting, and the surface must be free of deposits (barnacles, growth) and crevices or occluded surfaces." (These are "good" conditions.)

Originally Posted by At sea

Also, re para 1, how long would stainless need to be deprived of oxygen for the oxide skin to be lost? I ask that because stainless keel bolts are avoided for that reason, yet I've seen them come out in perfect condition after some years locked in timber and sikaflex.

The only data I have is from long-term tests for pitting of stainless steel plates left immersed in quiet seawater:
Type 304, 320 days, average pit depth under fouling: 0.56 mm, max 0.99 mm; in crevices: average depth 0.6 mm, max depth 0.91mm.
Type 316, 365 days, average pit depth under fouling: 0.3 mm, max 1.4 mm; in crevices: avg depth 1.4 mm, max depth 1.4mm.
Crevice and pitting corrosion require seawater - there won't be corrosion if the keel bolts stay dry.

Originally Posted by At sea

I guess what I'm querying is whether any anchoring chain could be buried and deprived of oxygen long enough to lose the protective skin. Wind and tide should ensure that all of it 'comes up for air' regularly.

Unfortunately, scratches won't heal in seawater. And you will have constant wear at every contact between every link, and there are rough spots where every link is welded.

You could use the chain until it starts to make you worry, but you'll need to regularly clean and inspect the whole chain carefully, with increasing frequency the longer it is submerged, which seems like a chore that would become more than tedious after a few meters. Not to mention tiring! That is a huge, heavy pile of chain. And worry you should - stainless DOES give way without "notice".

Originally Posted by At sea

And even then, why wouldn't it immediately reskin itself (oxide layer) once exposed to the oxygen in water?

In (clean) fresh (low chloride concentration), oxygenated water the oxide layer does reform.

[Wand]

Originally Posted by savoir

I use stainless chain for anchoring near home. The main section of chain is 250' G4 but it comes off the boat when I'm home and 40' of stainless goes on. Works for me. The bow floats 1" higher too. Clean chain + clean anchor locker + faster boat = happy owner.

I guess I'll put Savoir's experience together with Shipshape's detailed advice in the post above and try to make a judgement. Thanks to you both and others. As always, info feeds doubt, or 'the more you know, the less you know' etc. I'll chat to the chainmaker PWB next week and report any useful info back. Cheers.

[bangkaboat]

What is most important to consider in anchor chain is carbon content and shock load capability/yield strength. Anyone who has been past a shipyard/drydock will note that the cranes use wire, not chain (along with fibre slings). while galvanized wire rope would be a better choice - when one needs a rode that has abrasion resistant properties - storage can be a challenge, as would kinking, hence the continued use of chain. If one were only anchoring in areas where the weight on the chain was smoothly loaded and/or constant, stainless chain would be a viable option, imho. As this is rarely the case, the ability of rode to stretch to a high percentage of it's original length before reaching it's maximum yield point(the point at which it will no longer return to it's original length and remains deformed) is significant.

Because so few sailors re-measure their chain rode length, periodically, when buying a boat, I never consider a lot of chain inventory as a benefit because I have no idea of how old it is or how often or in what conditions it has been used. Therefore, I always expect to replace it.

[Mark Johnson]

Having sized appropriately and installed many thousands of pieces of boat gear & hardware, over the 40 years I've been building boats, I will continue to refer primarily to the SWL or WLL as GordMay's "Rosetta Stone" points out, in my outfitting decisions. There are just more things to take into play then its BL in a lab. For example, in anchor rope... With two similar sized samples of three strand, EACH with @ a 5,000 pound BL, but one is Nylon and one is Dacron... UNDERWATER, the Dacron is the same strength, but the Nylon has lost strength. This is from day one! Which one is more abrasion resistant? UV resistant? What form of rope construction becomes weaker when "pumped"? Etc...

The fact that Harken blocks are rated VERY differently (% of BL wise), than their competition, is another example. The equipment's manufacturer makes recommendations as to the suitable application of their product, including a theoretical load limit that should never be exceeded, (also finer details, like which lubricants to use or avoid)! Sometimes the SWL it is just a % of BL and sometimes all of the factors that I previously mentioned come into play.

My ACCO G-4 chain is now flaking badly and due for replacement soon, I can SEE this. If it fails the next time I use it, it's my fault! I suspect that 99% of galvanized chain failures are from not replacing it when one should. The same may be true of SS chain as well, except that replacement time is harder to discern, (if it is from "work hardening" rather than rust). BTW... Anchor rode lockers appear to be far more corrosive to galvanized chain than when it is under sea water. The seldom used end of my chain is by far the more rusty end, even though any nuisance water is trapped and pumped out from the screened sump below.

My SS 316 rigging wire, @ 15 years old, is beyond its suggested service life. It is also due for replacement. (although it looks perfect)... I will continue, in all of my replacement and outfitting decisions, to size things where the load never exceeds the WLL OR the SWL, and even then, watch them like a hawk.

I strongly advise to anyone, NOT to focus in on "lab condition" BLs, rather than the well researched suitability of that product in a given application. Instead, look closely at the product manufacturers WLL or suggested SWL, and don't exceed it. Years down the road, don't even come close!

I don't mean to offend anyone here... I am only trying to pass on useful information. Some may disagree, as has been the case in this discussion. They will have to live with their outfitting choices, just like I, as well as hundreds of my clients, will have to live with my decisions.

Good luck to us all!
Mark

[Wand]

I am the OP of this thread and a similar discussion has been running concurrently in another thread. Thought it best to copy my post from there to here, with apols...

I mentioned in an earlier post in this thread that I had come across some very cheap 13mm stainless by Australian chainmaker PWB, which by all accounts is a maker of quality products. Seems it was a bin end - they haven't made that chain for years.

I had intended to use it for mooring chain (that's what I went shopping for that morning) but there seems to be strongly held views on this and on another current thread that this is not a good idea. PWB do not endorse it for that purpose either. However, no-one has pointed (yet) to any first hand experience of stainless chain failure.

So might as well live dangerously. Since I've now got the chain, and there being no other useful purpose I can see to which it can be put, I'm prepared to settle the arguments with a practical test. I am going to use it for mooring chain, albeit for two light displacement vessels. The test will be super stringent given we have a power station outfall nearby and water temperatures are usually at tropical levels.

But I am not going to entrust the boats to the SS entirely; we have fore 'n' aft moorings here, and the forrard one will be the ever-reliable rod (so the boat won't escape entirely).

So stay tuned for a few months/years/decades and I'll let you know how the SS chain fares. Nothing like a real life observation to inform the theory.

[craigsmith]

Nobody really argues that 316 stainless is appropriate for moorings. Permanent submersion, heavy chain mostly buried in mud, and the same length of chain always at the surface is bound to permit rapid corrosion. The hotter and saltier the water the poorer the scenario. You're not going to prove much when you see deterioration.

On the other hand 316 stainless for anchor chain is quite okay because the way it is used results in different conditions for the metal. Duplex would be better but everyone seems to get away with 316.

[Wand]

Originally Posted by craigsmith

Nobody really argues that 316 stainless is appropriate for moorings. Permanent submersion, heavy chain mostly buried in mud, and the same length of chain always at the surface is bound to permit rapid corrosion. The hotter and saltier the water the poorer the scenario. You're not going to prove much when you see deterioration.

On the other hand 316 stainless for anchor chain is quite okay because the way it is used results in different conditions for the metal. Duplex would be better but everyone seems to get away with 316.

OK, I think I follow the theory; the plan is to test it. Maybe there'll be some surprises, and maybe not. Nothing will be lost.

From my experience, the wear on normal galv mooring chain is mainly in the shackle and the first few links below the float. Checking the state of these bits normally tells the story of the rest of the gear. Occasionally though there is also extra wear at the weights end - that could be for a range of reasons, including just that it is a short bit of chain and gets worn with every tide. Or whatever; we still pull them right up to check.

We get quite reasonable tides here, and not much if any chain will be permanently buried in mud. The bottom bit will come up for air (water) mostly twice daily. Will that be enough? Don't yet know.

In moorings, it's not so much the breaking loads that are a concern; it's more how resistent the chain is to wear. A certain type of steel will wear at the same rate regardless of how thick it is, and so the thicker the chain, the longer it will last.

That's why I usually try to find 20mm chain or rod; that's miles in excess of breaking loads but gives me a good many years of wear. I also like to add a few links of 30mm chain just under the float, since this is where the main wear occurs. The advantage of rod btw is that it's easy to weld on an additional arc to double the wear life.

I'm no metalurgist but I'd guess that the stainless links near the surface in this test setup would to wear slower than normal galv steel of the same gauge. How much slower? Again, don't yet know.

But riding alongside this query is whether the crevice corrision and work hardening and brittleness and all of the other problems that condemn stainless chain in this usage will become issues sooner than the wear issue. And if so, how much sooner.

And over all of this is the electrolysis issue. I'm not quite mad enough to empty my pockets to get some stainless shackles of the right size to counter this potential degradation factor. Unless someone wants to donate some for the test, that'll just have to be factored in via close inspection and a little guesswork.

As I mentioned earlier, the test will take place in waters usually over 30C, thanks to the nearby power station. The educated guess would be that the theory, unlike the chain, will hold. But time will tell...